1. Field of the Invention
The invention relates generally to a leaded aviation fuel lead scavenging additive formulation that is relatively less toxic and more easily transported and handled than existing formulations.
2. Background
Lead scavenging additives for leaded aviation gasoline help to prevent lead deposits in the combustion chambers of piston engined aircraft. These deposits can prevent proper operation of the spark plugs and cause rough running of the engine, loss of power, etc. The use of tricresylphosphate (TCP) in additives for leaded aviation gasoline aircraft fuel (including one hundred octane low lead, 100LL) is known. The lead is added to fuel as tetraethyl lead by the gasoline maker, and the rate of addition is prescribed by the FAA (Federal Aviation Administration). The concentration can be from 2 milliliters/gallon fuel to 4 milliliters/gallon fuel, depending on the formulation. The use of polyether amines (PEA) in additives for automotive fuels is known. This is taught in U.S. Pat. No. 4,247,301 dated Jan. 27, 1981. PEA is not, however, described for aviation use. The use of polyisobutylene (PIB) and polyisobutylene amine (PIBA) in additives for automotive fuel is known, but also not for aviation use. Similarly, the use of glycol ether in additive mixtures for automotive fuel is known, but not for aviation use. This is taught in US Patent Application 2005/0268540 dated Dec. 8, 2005.
The most common piston engines for light aircraft are made by Lycoming, Rotax or Continental. Lycoming engines are made by a division of Textron and Continental engines are made by Teledyne. Rotax engines are made by a division of Bombardier. TCP has been used for three decades as an ingredient in an additive for aircraft leaded aviation gasoline (including 100LL, one hundred octane Low Lead), always added by the operator of the aircraft. It is not added by the distributor of the fuel. TCP additive helps prevent lead deposits on spark plugs. These deposits, which appear as gray lumps, are conductive to high voltage and bridge the electrodes on the spark plug, preventing a spark and rendering the spark plug inoperative. The deposits are mostly lead oxide. The TCP works by converting the lead to lead phosphate which is not conductive. Lead phosphate also has a higher melting point (800 to 1014 degrees C.) than lead oxide (370 to 886 degrees C.) and is therefore preferentially blown out with exhaust gasses. However, some of the lead phosphate created is not ejected from the engine and remains in the combustion chamber. This deposit then forms the base on which oily deposits can build up.
Plug fouling is mostly observed during ground operations prior to take-off. The accumulations occur mostly when fully rich mixtures are set for low power engine operation, a standard procedure during taxiing.
The acronym TCP was trademarked by Alcor Inc. and the product marketed as Alcor TCP. It contains TCP and toluene (flash point below 140 degrees F.) and is specifically banned from being carried in the cockpit of aircraft during flight because of the toluene content. It cannot be easily shipped by common carrier for the same reason.
Existing solutions for preventing or mitigating lead deposits in combustion chambers work well enough. But aircraft are traveling machines, and if it is not possible to carry this material in the cockpit then the pilot faces the problem of spark plug fouling and rough engine running at intermediate airport re-fuelling stops. This is potentially a dangerous situation with some engines. What is required is a formulation which allows the pilot to safely carry this material in the cockpit.
Furthermore, obtaining a lead scavenging mixture from a vendor is made much more difficult if the material is toxic or extremely flammable. The vendor may charge a high premium for shipping such a material and the carrier, such as UPS or FedEx may outright refuse to ship it.
Existing solutions were simply formulated too long ago, about thirty-five years, to meet the requirements of today's pilots.